Stabilized phosphonitrile elastomers

ABSTRACT

The stabilization of phosphazene polymers against degradiation when exposed to temperatures of about 275*F or higher, in air is achieved by the addition of controlled amounts of stabilizers to such phosphazene polymers, metal dialkyl-,alkyl-aryl-, or diaryl dithiocarbamates of zinc, lead or bismuth, or various inorganic or metallo-organic compounds, being preferred stabilizers.

United States Patent [191 Kyker et a1.

1 1 Oct. 22, 1974 STABILIZED PHOSPHONITRILE ELASTOMERS [75] lnventorsz Gary Stephen Kyker, Uniontown;

Joseph Alfred Beckman, Akron; Adel Farhan Halasa, Bath; James Edward Hall, Barberton, all of Ohio [731 Assignee: Firestone Tire & Rubber Company,

Akron, Ohio [22] Filed: May 10, 1973 [21] AppL No.: 359,034

[52] US. Cl 260/45.75 R, 260/2 P, 260/45.7 R,

260/45.75 B [51] Int. Cl C08g 51/56, C08g 51/62 [58] Field of Search 260/2 P, 45.75 R, 551 P,

260/37 N, 23 R, 45.7 R; 117/161 UA [56] References Cited UNITED STATES PATENTS 2/1953 Caldwell et a1. 260/23 9/1966 Evans 26(1/2 5/1967 Scullin et a1. 2611/23 OTHER PUBLICATIONS Chemistry and Engineering, April 22, 1968, periodical, pp. 68-81.

Primary Examiner-V. P. Hoke 5 7 ABSTRACT 7 Claims, 4 Drawing Figures Dilute Solution viscosi.

Dilure Solution Viscosity PATENTED 0m 22 i974 SHEET 20? 2 FIG. 2

.25 ole "/0 Dieihyl trol biliz Aqinq Time@300F. (Hrs) *i iifiiinc Dieihyl Diihiocurbomofe Aqinq Ti me @300" E (Hrsi) 1 STABILIZED PHOSPHONITRILE ELASTOMERS This invention relates to the stabilization of phosphonitrilic elastomers, fibers and plastics against thermal degradation. The invention is applicable to the phosphonitrile fluoro-esters described in US. Pat. No. 3,271,330 (Evans) issued Sept. 6, 1966, the phosphonitrile polymers described in US. Pat. No. 3,370,020 (Allcock et al.) issued Feb. 20, 1968, the phosphonitrile elastomers described in US. Pat. No. 3,515,688 (Rose) issued June 2, 1970 and the phosphonitrile terpolymers, copolymers and homopolymers described in US. Pat. Nos. 3,702,833 (Rose et al.) issued Nov. 14, 1972 and 3,700,629 (Reynard et al.) issued Oct. 24, 1972 and to other polymers characterized by a repeating sequence of r "l Li J.

(n 3 to 10,000 or more) units in which various groups are attached to the P atoms, such groups including alkoxy, fluoroalkoxy, aryloxy, amino, arylakoxy, and other groups, and the phosphazenes described in a recent article on phosphazene chemistry in Chemical Reviews 1972, Volume 72, No. 4, particularly pages 349-356.

The polymers to which the present invention applies includes both elastomers and thermoplastic materials. Such polymers exhibit a number of desirable properties but are found to degrade when exposed in air to temperatures of the order to about 275F or 300F or higher for prolonged intervals of time.

A principal object of this invention is to modifysuch polymers by the addition thereto of controlled amounts of specified materials selected from the group consisting of metal oxides, hydroxides, carbonates, alkoxides, aryloxides and other organo-metallic compounds including particularly metal dialkyl-or diaryldithiocarbamates of divalent metals such as zinc, lead and bismuth.

The amount of stabilizer used depends to some extent on the stabilizer utilized, and on whether more than one stabilizer is used. In general the amount of sta-' bilizer is as shown in the following Table:

Table l Stabilizer Amount 1. Metal Dialkyl-. Alkylaryl-, or

Diaryl Dithiocurbamates 0.01 5 mol 2. Group 1A Hydroxides or carbonates 0.01 3 mol 3. Metal Oxides 0.5 20 weight 4. PVC Type Stabilizers (lead oxides, 0.25 6.0

metal soaps and organotin mercaptides) weight nation of any of these structures, halogen atoms or various other substituents being attached to the P atoms, e.g. as described in the patents noted above and in other literature on phosphonitrilic polymers.

One presently popular method for preparing such polymers involves first preparing [NPCl h oligomers wherein x is a small integer, and heating the oligomer to obtain higher molecular weight products. These products, are such, or after purification and upgrading, are then reacted with one or more suitable alkoxides, fluoralkoxides, aryloxides, or with other materials which replace some or all of the chlorine atoms in the polymer, with the reactive group of the alkoxide or other reactive group of the alkoxide or other reactant.

Whatever the reason for the tendency of the polymers to degrade when exposed to relatively moderate temperatures for prolonged time intervals, it has now been found that the incorporation of selectively small amounts of stabilizers into the reacted polymer produces products in which the thermal stability is greatly improved as compared with the unstabilized material. This invention applies also to fully compounded and cured stocks of these elastomers.

A particularly preferred class of stabilizers are the metal dithiocarbamates represented by one-of the following formulae:

:LM :laBi

wherein M is a divalent metal selected from the group consisting of Zinc and Lead and each of R and R represents an alkyl or aryl group and R and R are not required to be the same.

FIGS. 1 to FIG. '4 are graphical representations showing the improvement in stability conferred in a copolymer in which CF CH O and HF- C(CF );,CH O- groups are randomly attached to the P atoms in a 1:1 ratio by the incorporation therein of small amounts of metal dialkyl dithiocarbamates and Group 1A Bases.

FIG. 1 is a graph illustrating the stabilization achieved in phosphazenes in which the groups attached to the phosphorus atoms are -OCH CF;, and OCH (CF CF H with the addition of 0.75 mole percent zinc dimethyldithiocarbamate and 0.75 mole percent zinc dibutyldithiocarbamate.

FIG. 2 is a similar graph illustrating the effect of the addition of various amounts of zinc diethyldithiocarbamate on the thermal degradation of the same polymer as that in HO. 1.

FIG. 3 is a similar graph showing the effect of the addition of various amounts of bismuth dimethyldithiocarbamate on the thermal degradation of the same type of fluoralkoxy phosphazene polymer.

FIG. 4 is a similar graph showing the stabilization achieved by the addition of rubidium and potassium carbonates to the same phosphazene polymer.

Tables l-XV present additional data illustrative of the invention.

Table 1 (See FIG. 1)

Aging of Elastomer '1 Cumml nu addition 11 with 0.75 nml '4 zinc dimclhyldithiucurhzmnuc 111 with 0.75 mu] .4 wine dihmyldilhinczirhunmtc Physical Sum:

E Elnsmrncr M Mcll F Flaw TABLE IL-iJsV 1N ACETONE After aging 02 05 (T) PFAP with various stabilizers Aging time at 300 F. 7 (hrs.) 28 31-1 31-2 31-11 31-12 31-13 31-14 31-15 31-16 31-17 31-18 -3A 26-7 26-8 26-1) 26-10 NOTE.See Table III for Code.

I I Table 111 Table V 5 Dilhiocarbumute 35 HEAT AGING OF ZIMATE-TREATED POLYMERS Sample Mole Number Dithiucarbamme A11 Stocks Consistcd 01' 100.0 Polymer.

. 20.2 Filler and 7.5 Curutive 28 None R 175- 388 389 376 31-1 1.0 bismuth diulkyl polymer A 31-2 3.0 bismuth druikyl 40 polymcr B mm 31-11 1.0 1*'dd"lkl 31 12 3.0 lgd dang Polymer C 1011.0 l l Normal StressZSlruin Q05 -cured 24 hrs. at 212F '8 1" 31";0 Cure Time (min./F) /300 /300 60/280 311% :1? z i M (psi) 920 585 545 I Tensile (p51) 1305 1340 1520 31:; {0 g gg 45 Elongation Egg Eg 3 Zinc dimcthyi Aged siresslslrain 30UF aging 26-11 0.31 zinc diethyl 12 'Y' 490 61 0 no 26-9 0.23 zinc dibutyl E y 6-10 0. 5 lead dialkyl 335 72 hrs. 335 450 240 ,TABLE IV.THE EFFECT OF MODE OF MIXING METAL DITHIOCARBAMATE WITH C g, 0% (T) PFAP ELASTOMER ()N THERMAL STABILITY (300 F. IN AIR) Aging Pertime cent- Sample Stabilizer Stabilizer level Mode of mixing (hrs.) Nature of sample DSV 3 gal 0.0 Elastomer: 3. 48 24. 5 1. 15 52. S 0. 01 196. 8 0. 33 Zinc dibutyl 0.03 wt. percent Treated acetone solution of polymer with 0.0 3.41 dithioearba- Zn, 0.003% 0.80 mole percent of butyl zimate-poiymer 24. 5 1. 38 mete. Na' 0.15% CI. coaguiated by addition to Waterdried in 52.8 1.18 vacuo at 25 C. 196. 8 0. 05 Zinc dibutyl 0.09 wt. percent Same treatment as Io1yrner B except that 0.0 Green olastomer. 3. 28 0.0111

dithioczirbe- 211 0.007% solvent stripped from polymer 1 by air 24. 5 S1ight mn1t 1. 35 all mate. N99, 0.0% Ci". drying then 0 hrs. in vacuo at 30 C. 52. 8 1o. 1.07 mm- 196. 8 M011; and flow 0.111 ples. 7 inc dibuty1 0.02 wt. percent Same treatment as Polymer B except poly- 0.0 Brown slinky elastomnr. 1.60 dithiocarba- Z112", 0.007% rnrr l heated at 150 C. for 2 hrs. in vacuo. 4. 5 1.2 1 male. Na .0.0% (31-. .8 ,,(1n 0.78

.8 M011 :uu1110w 0. 80 Zine dibutyl 0.012 W1. percent C2, (15* polymer (100 gr, in 0001mm), was 0 1210001001. 3. 01 dithioearba- Zn. stirred with hntyl zirnate (2 g.) Inr 3 days :11. 8 No 111011.. 2. 01 mate. 1 25 11. The polymer was conguialwl by d )1. 1. 0n addition to n-hexmm and dried in vncno 210.3 ..r10.. 1. K8 00 (1. for 16 hrs. 28-1. 3 N0 mell. still tough 1. 73

elnslmnvl.

1 (3, 0 01) polyfluoreaikoxyphosphazene. 2 A second sample of C 0 (T) polyfluorozrikoxyphosphazene. K As measured in acetone.

Table V Continued Table Vll v THE EFFECT OF BUTYL ZlMA'l'E LEVEL ON THE THERMAL HEAT AGING F ZIMATE-TREATED POLYMERS STABlLlTY OF C0. C PFAP ELASTOMER AT 300% IN AIR All Stocks Consisted of 100.0 Polymer, Bury] 20.2 Filler and 7.5 Curative Zimme Aging .Levcl Time Sample I20 hrs. 255 350 210 (Mole '71) (Hrs) Nature of Sample DSV" Number 192 hrs. I95 260 153 4 Control 0.0 Elastomer 2.43 l Tensile 19st) Control 47.4 Melt and llow 0.47 -l 24 hrs. 985 1245 7|0 Control l64.4 Melt and flow -2 718) Ers- Control 243.9 Melt and flow 0 l6 -3 rs. 120 hrs; 385 648 270 0.36 0.0 Elastomer 2.40 2 l92hrs. 270 445 190 0.36 47.4 No melt 0.92 -l 0.36 164.4 No melt 0.55 -2 64 lilon ation is 0.36 243.9 Slight melt 0.44 -3 4 hrs. 158 l50 I85 48 hrs. l65 155 l83 0.72 0.0 Elastomer 2.40 3 72 hrs. 135 145 l45 0.72 47.4 No melt 0.77 -l 120 hrs. I60 I68 l50 0.72 164.4 No melt 048 -2 192 hrs. 155 I85 135 0.72 243.9 No melt 0.60 -3 L64 0.0 Elastomer 2.79 4 Polymer A A C C 'tTl polymer treated with NaOH and 2 parts Butyl Zimate. fi gl j t l l e t an ow =Polymer B A C t'l'l polymer treated with 2 parts Butyl Zimate. 1.64 243.9 Melt and flow 0.35 -3 Polymer C A C':. CQtT) polymer untreated.

3.28 0.0 Elastomer 2.39 5

3.28 47.4 Melt and flow 0.62 -l 3.28 164.4 Melt and flow 0.40 -2 3.28 243.9 Meltand flow 0.36 -3 4.92 0.0 Elastomer 2.68 6 4.92 47.4 Melt and flow 0.70 -l 4.92 I644 Melt and flow 0.50 -2 4.92 243.9 Melt and flow 0.36 -3 'C C, Polyfluoroalkoxyphosphazene Table As measured in Freon TA IMPROVED AGING STABILITY OF POLYFLUOROALKOXY PHOSPHAZENE VULCANIZATES PREPARED Table Vlll FROM POLYMERS TREATED WITH DlALKYL-DlTHlO 35.

CARBAMATES THE EFFECT Ol- BUTYL ZlMAlE ON THE RATE or S. l A: C4 D5 DEPOLYMERIZATION OF -.Cfl PFAP ELASTOMER AT 300F IN AlR Stress-Strain Properties Bu I y l00% Modulus 19st! Aged. Hrs. at 300F zlmine Agmg o 545 585 940 550 f fi f l 24 330 M0 660 600 0e 1) (Hrs) aturt. o ample Num Ll" 48 235 440 690 v 11 140 450 585 440 8:5 231% Elllllll 1 1 1 0.2 47.x No melt 0.85 -2 0.2 73.1 No melt 0.85 -3 Tensile Si 0.2 l43.l No melt 0.57 -4 Aged m 300 Control 0.0 Slight melt 3.03 8

.0 l5..0 I340 1765 2325 n t 24 7) I245 I260 [600 Control .5 Melt and How 0. )9 -l 48 390 860 950 Control 423 Melt and flow 0.7I -2 300 710 Control 53.0 Melt and flow 0.56 -3 6 270 648 1 b Control l35.3 Melt and flow 0.l5 -4 I92 190 445 510 61 3 Sui Properties A C C, Polytluoroalkos plmshpa/ene elastomer 100% vodulus (psi) -'As measured in Freon 'l'A Aged. Hrs. at 300F 7r Elongation I 55' Aged, Hrs. at 300F Table [X 0 l50 I45 I30 153 24 185 l50 I40 180 48 183 l55 l23 THE EFFECT OF SELECTED ALKYL ZlMA'l'ES ON 'l'Hli 132 145 M5 135 I RATE OF DEPOLYMERIZATION OF C. -.C', PFAP ELASTOMER' 0 I35 I I40 210 l92 I35 I85 140 203 60 Aging Alkvl Level Time Nature of Sam le P Zimate (Mole 7r) (Hrs.l Sample DS\"-' Number All stocks contained l00 polymer. 20.2 tiller and 7.5 curative; All except B were l cured 60' at 280F. B was cured at 300F Polymer A is C C lTl Polyfluoroalkoxyphosphalene elastomer Methyl 0.3 0.0 Elastomer 2.64 9 Polymer B is identical to Polymer A except it was treated with 2.0 phr of Butyl Zinta'te 23.3 No melt l.74 'l Zimate in acetone solution followed by coagulation of the polymer with hexane. 65 62.8 No melt 0.94 -2 I 87.8 No melt L03 -3 Polymer C is a C (TAT) polyfluoroalkoxyphosphazene elastomer 1 ,3 N mu (UH Polymer D is identical to Polymer C. except it was treated with 0.] mole I of 1071) N (L( .5

methyl vimate in acetone solution followed by evaporation of the solvent.

Table XII Table IX Continued THE EFFECT OF SELECTED ALKYL ZIMATES ON THE RATE OF DEPOLYMERIZATION OF (l C PFAP THE EFFECT OF CESIUM HYDROXIDE 1 MOLE on ON THE THERMAL STABILITY OF (1.0,

A C'- C. Polylluroarlkoxyphosphozcnc cluslomcr A5 measured in Fr uon Table X (Hm) Stabilizer Aging [DSV l' Appearance of Sample Sample Level Time at Number (Mole 71) -300F l3-2-6 Control White Elustomer 2 L09 Melt and flow 4 0.86 Bud melt and flow, degraded 24 0.62 Bad melt ilfld flow, degraded 48 0.44 Degraded and very sticky l4-2-l 0.5 0 3.42 White Elastomcr 0.5 2 l.7l White Elustomer 0.5 4 1.00 White Elaistomer 0.5 24 0.43 Tun, melt and llow 0.5 48 0.24 Tun. sticky and degraded 15 2-2 L0 0 2.35 White Elastomcr L0 2 1.94 While Elastomcr L0 4 LI} White Elaslomcr 1.0 24 0.65 Tun Eluslumer. melt and slight flow L0 48 0.28 Tun Elastomer, melt and slight flow l6-2-3 2.0 0 3.I(l White Elzislomer 2.0 2 l.7l While Elustorncr 2.0 4 1.4) White Eluslomcr 2.0 24 L00 While tun clustomer. slight melt 2.0 48 0.69 White tam clastomcr. slight melt IDSVI Dilute Solution Viscosity measured in THF. 'Visual inspection of samples when removed from 300"} oven.

Table XI 55 THE EFFECT OF ALKALINE BASE PRETREATMENT ON THE THERMAL STABILITY OF C( Cfl PFAP ELASTOMER' AT 300F IN AIR U C, Pollluurozilkoxyphosplmzem:) Elttalomur '-'In Freon TA.

E S OME ELASTOMER' A i Aging Alkyl Level Time Nature of Sample Sample Zlmate (Mole (Hrs.) Sample DSV Number Number (Hm) Sample (M I 19-] 0.0 Elustomcr 2.80 0.0 Ethyl 0.28 0.0 Elustomcr 2.76 10 Nu l 1.41: 0.0 Zimutc 23.3 No melt L47 -l mvll L52 0.0

62.8 No melt 0.77 -2 No mm 1.54 0.0 87.8 No melt 0.74 -3 1 I12 No melt t5} (H) lll.8 No melt 0.64 4 231.5 Mel! and How 083 (L0 207.0 No melt 0.43 -5 20-l-B 0.0 Eluslomcr 2.75 0.0 Butyl 0.20 0.0 Eluslomcr 2.59 I 1 (Cfln- 23.5 Slight melt 1,0} 0.0 Zi 133 N me og troll 53.0 Mull and flow 0.5] 0,0 (118 N mgll (L71 .2 92.5 Depolym. 0.25 0.0 87.8 No mg (L56 -3 l4l.5 Dcpulym. I [7 0.0 l I 1.8 No melt 0.64 -4 207.0 Slight melt 0.38 -5 A (0.0 Pol (lluoronlkoxyphmpha/vnu) ClllhtilllL'l'. Control 0.0 Elnslomer 2.75 l 2 s in n Control 22.5 1.03 -1 Control 530 0.5l -2 Control 92.5 0.25 3 Control I4l.5 0.17 -4 Table XV THE EFFECT OF SELECTED GROUP l BASlC I COMPOUNDS ON THE THERMAL STABILITY OF C ,C (Tl PFAP ELASTOMER' (300F lN AlR) Stabilizer Aging Sample Level Time Number Stabilizer (Mule 94) (HRS) Nature of Sample DSV 39-3-14 Control 0.0 Elnstorner 3.03 23.3 No melt L06 42.3 Melt 0.7l i35.3 Melt and flow 0.15 4U-1-A CsOH 1 0.0 Elastomer 3.06 48.0 N0 melt 2.24 -2 174.8 Melt and flow 1.44 -3 345.8 Melt and flow 0.84

41-1-8 CSOH 3 0.0 Elustumer 3.45 -1 48.0 Slight melt 1.49 -2 174.8 Melt and flow 1.14 .-3 345.8 Melt and flow 0.52

'42-2-A Cs CO 1 0.0 Elastomcr 3.17 -1 4210 No melt 2.65 -2 174.8 Slight melt 1.13 -3 345.8 Bad flow 0.55

43-2-13 (Is ,CO; 3 0.0 Elastomer 3.62 -l 48.0 No melt 2.37 -2 174.8 Slight melt 1.51 -3 345.3 Bud flow 0.52

44-3-A m co 1 0.0 Elustomcr 3.69 -1 48.0 No melt 2.72 -2 l74.8 Slight melt 1.89 -3 345.8 Slight melt 116 45-3-8 Rh CO; 3 0.0 Elastomer 3.77 -1 48.0 No melt 3.02 -2 174.8 Slight melt 2.33 3 345.8 Slight melt 1.61

46-4-A RhOH l 0.0 Elastomcr 4.64 -1 48.0 No melt 2.70 -2 174.8 Slight melt 1.49 -3 345.8 Slight melt (1.61

. 47-4-13 RbOH 3 0.0 Elastomcr 5.98 -1 48.0 No melt 3.16 -2 l74.0 Slight melt l.4l -3 345.2 Slight melt 48-5-A v KOH l 0.0 Elastorncr 6.08 -1 75.0 Slight melt 2.12 -2 174.5 Melt and flow 1.38 -3 246.0 Melt and flow 0.33

49-5-13 KOH 3 0.0 Elastomcr 5.40

-1 75.0 No melt 2.91 2 i745 Slight melt 1.57 -3 246.0 Slight melt 0.93

50-6-A K CO l 0.0 Elnstomer 3.40 -.l 75.0 No melt 2.96 -2 174.5 Slight melt 2.35 -3 246.0 Slight melt LXI 51-6-8 K. .CO 3 0.0 Elustnmer 3.87 -1 75,0 No melt 2.86 -2 174.5 Slight melt 2.40 -3 246.0 Slight melt 1.84

l. A tfll'l'i Pnlytl'ltmruatlknxyphusphu/cncl I 2. As measured in acetone.

in the preceding description the formula C has been OCH (CF ),,-,-H. used to designate monovalent radicals (side chains) The symbols C and d) are intended to represent alkhaving the formula -O(CH )-(CF ),,,-F. oxy and aryloxy side chains, C standing for amyloxy Thus C represents OCH ,CF C represents and d) standing for phenoxy. OCH CF CF etc. 65 Finally the term zimate" is intended to mean dithio- Another abbreviation used was C,,'(T) which corcarbamate.

responds to monovalent radicalshaving the formula The polyphosphazenes to which the present invention is applicable include those described in US. Pat. Nos. 3,271,330 (Evans); 3,370,020 (Allcock et al.); 3,515,688 (Rose): 3,702,833 (Rose et al.) and 3,700,629 (Reynard et a1.) and in Chemical Reviews 72 (4) 1972, particularly pages 349356 including the polyphosphazenes as elastomers, thermoplastic elastomers, plastics, fibers or films.

Instead of the dialkyl dithiocarbamates of zinc, bismuth, and lead other dialkyl dithiocarbamates which are suitable include those of metals selected from Groups llA, llB, IVA, lVB, VA and VB of the Periodic ELJ Ll I

in which each R and R' is a group which renders the units resistant to hydrolysis and which is selected from the group consisting of alkoxy, substituted alkoxy, aryloxy, substituted aryloxy and amino in which not every R and R is the same as every other R and R, and n is an integer greater than 3 and less than about 50,000; and a stabilizer selected from the group consisting of 1 between 0.01 and 5.0 mole percent based on the polyphosphazene of at least one dialkyl, alkylaryl-, or diaryldithiocarbamates of a metal se lected from the group consisting of zinc, bismuth and lead, and 2. between 0.01 and 3 mole percent based on the polyphosphazene of at least one basic inorganic compound of a metal selected from the group consisting of alkali metals and alkaline earth metals including Mg.

2. The stabilized polyphosphazenes of claim 1 wherein R and R are each fluoroalkoxy groups.

3. The stabilized polyphosphazenes of claim 1, stabilized with a zinc dialkyldithiocarbamate.

4. The stabilized polyphosphazenes of claim 1 wherein the basic inorganic compound is selected from the group consisting of metal oxides, hydroxides, and carbonates.

5. The stabilized polyphosphazenes of claim I as a constituent of a composition containing a gum polymer of a compounded stock material.

6. The stabilized polyphosphazenes of claim 1 wherein the incorporation of stabilizer is effected in homogeneous solution.

7. The stabilized polyphosphazenes of claim I wherein the incorporation of stabilizer is effected by mechanical mixing.

W050 UNITED STATES PATENT OFFICE (5/69) CERTIFICATE OF CORRECTION Patent: No. 5, 5,596 Dated October 22 197- Inventor(s) Gary Stephen Kyker, Joseph Alfred Beckman,

Adel Farhan Halasa, Edward Hall It is certified that error appears in the above-identified patent and that: said Letters Patent are hereby corrected as shown below:

In Column 5, Line 20, Table v In formula "Polymer A Ac C (T) should be --Polymer A AC (i ('19-- In Column 5, Table VI, Lines 52, 55, 5 "Stress-Strain 0 Properties, 100% Modulus (ps1) Aged, Hrs. et 500 F" I should be deleted. In Column 8, Table XII Line 6 "Aging" should be over word "Time" in next column of Table XII,

igned and sealed this 1st day of April 1975.

(SEAL) Attest:

' C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer 'and Trademarks 

1. A THERMALLY STABILIZED COMPOSITION COMPRISING POLYPHOSPHAZENES THE SKELETAL CHAINS OF WHICH CONSIST OF RECURRING UNITS REPRESENTED BY THE GENERAL FORMULA:
 2. The stabilized polyphosphazenes of claim 1 wherein R and R'' are each fluoroalkoxy groups.
 3. The stabilized polyphosphazenes of claim 1, stabilized with a zinc dialkyldithiocarbamate.
 4. The stabilized polyphosphazenes of claim 1 wherein the basic inorganic compound is selected from the group consisting of metal oxides, hydroxides, and carbonates.
 5. The stabilized polyphosphazenes of claim 1 as a constituent of a composition containing a gum polymer of a compounded stock material.
 6. The stabilized polyphosphazenes of claim 1 wherein the incorporation of stabilizer is effected in homogeneous solution.
 7. The stabilized polyphosphazenes of claim 1 wherein the incorporation of stabilizer is effected by mechanical mixing. 